WASHINGTON — In what may be the biggest such scandal in Air Force history, 34 officers entrusted with land-based nuclear missiles have been pulled off the job for alleged involvement in a cheating ring that officials say was uncovered during a drug probe.

The 34 are suspected of cheating several months ago on a routine proficiency test that includes checking missile launch officers' knowledge of how to handle an "emergency war order," which is the term for the authorization required to launch a nuclear weapon.

The cheating scandal is the latest in a series of Air Force nuclear stumbles documented in recent months by The Associated Press, including deliberate violations of safety rules, failures of inspections, breakdowns in training and evidence that the men and women who operate the missiles from underground command posts are suffering burnout. In October the general who commands the nuclear missile force was fired for engaging in embarrassing behavior, including drunkenness, while leading a U.S. delegation to a nuclear exercise in Russia.

The AP disclosed in May an internal Air Force email in which a missile operations officer complained that his force was infested with "rot" — bad attitudes and disregard for discipline.

A "profoundly disappointed" Air Force Secretary Deborah Lee James, the service's top civilian official, told a hurriedly arranged Pentagon news conference Wednesday that the alleged cheating at Malmstrom Air Force Base, Mont., was discovered during a previously announced probe of drug possession by 11 officers at several Air Force bases, including two in the nuclear force who are among the 34 suspected of cheating.

"This is absolutely unacceptable behavior," James said of the cheating, which Gen. Mark Welsh, the Air Force chief of staff, said could be the biggest such scandal in the history of the missile force.

"We do not know of (another) incident of this scale involving cheating in the missile force," Welsh said.

A spokesman for Defense Secretary Chuck Hagel said the Pentagon chief, who just last week visited a nuclear missile base and praised the force for its professionalism, was "deeply troubled" to learn of the cheating allegations. The spokesman, Navy Rear Adm. John Kirby, said Hagel insisted he be kept apprised of the investigation's progress.

Robert Gates, the former defense secretary who fired the Air Force's top civilian and uniformed leaders in 2008 after a series of nuclear weapons mistakes, called the exam cheating and drug investigations "very troubling to me."

"It does raise the larger issue of whether the systemic shortcomings and problems we identified in 2008 have been corrected, as I thought they had been, or whether there is still significant room for improvement," he told CNN's "Piers Morgan Live."

Sen. Mark Udall, D-Colo., urged Air Force leaders to take swift and decisive action to ensure the integrity of the nuclear mission.

"There simply is no room in our Air Force, and certainly in our nuclear enterprise, for this type of misconduct," said Udall, the chairman of Armed Services' strategic forces subcommittee.

Rep. Howard "Buck" McKeon, chairman of the House Armed Services Committee, said he has confidence in the majority of men and women in the missile force.

"I'm saddened that a few serious violations have sullied the name of an otherwise honorable group of professionals," McKeon said.

James said she will travel to each of the Air Force's three nuclear missile bases next week to learn more about conditions within the missile launch force and the more senior officers who manage them. She suggested that the cheating was confined to this single case involving 34 officers, although numerous missile officers have told the AP confidentially that some feel compelled to cut corners on their monthly proficiency tests because of intense pressure to score at the highest levels to advance in the force.

"I want all of you to know that, based on everything I know today, I have great confidence in the security and the effectiveness of our ICBM force," James said. "And, very importantly, I want you to know that this was a failure of some of our airmen. It was not a failure of the nuclear mission."

James, who has been in the job only four weeks, said the entire ICBM launch officer force of about 600 will have been retested by the end of the day Thursday.

Welsh said he knew of no bigger ICBM cheating scandal or launch officer decertification in the history of the missile force, which began operating in 1959. Last spring the Air Force decertified 17 launch officers at Minot Air Force Base, N.D., for a combination of poor performance and bad attitudes; at the time the Air Force said it was the largest one-time sidelining of launch officers. It later said 19 had been decertified; they were held off the job for two months of retraining.

Welsh said one launch officer at Malmstrom was found to have sent one or more text messages to 16 other launch officers with answers to their test. He said further questioning at Malmstrom determined that 17 other launch officers "self-admitted to at least being aware of material that had been shared. We don't yet know how or if each of those officers used that material, but we do know that none of them reported the incident to their leadership."

There are about 190 ICBM launch officers stationed at Malmstrom.

Welsh said the probe continues. "People at every level will be held accountable if and where appropriate," the general said.

The Air Force's nuclear mission includes operation of 450 Minuteman 3 intercontinental ballistic missiles. The 341st Missile Wing at Malmstrom, where all 34 suspected cheaters are based, is responsible for 150 of the 450 ICBMs. The 34 are junior officers: second lieutenants, first lieutenants and captains. Of those 34, two also are implicated in the drug probe.

The Air Force operates Minuteman 3 missiles at two others bases: F.E. Warren in Wyoming and Minot.

The Malmstrom unit failed a nuclear safety and security inspection in August but succeeded on a redo in October. Welsh said the alleged cheating took place in August or September; he said other details could not be released because the matter remains under investigation by the Air Force Office of Special Investigations.

The drug investigation that led to the discovery of alleged cheating was disclosed by the Pentagon last week. It said then that it involved 10 officers at six bases — five in the U.S. and one in England. On Wednesday the Air Force said the number of suspects has grown to 11. Welsh said he could not comment further on the drug probe.

James said that the ICBM force "needs attention" and that while immediate corrective action is being taken, Air Force leaders are planning to address some longer-term initiatives.